Injection modelocked Ti-sapphire laser with discretely variable pulse repetition rates to 1.56GHz

Abstract

A gain-switched diode laser was used to injection modelock a Ti-sapphire laser. The pulse repetition rate of the modelocked Ti-sapphire laser was varied by setting the diode laser pulse repetition rate equal to different multiples of the Ti-sapphire laser cavity fundamental frequency. Pulse repetition rates from 223 MHz (fundamental) to 1.56 GHz (seventh harmonic) were observed. No intracavity modelocking device was required and the Ti-sapphire laser cavity length was not changed. Maximum average output power at 854 nm was 700 mW for all pulse repetition rates when pumped with 6 W from an argon-ion laser. Pulsewidths ranged from 21 to 39 ps (FWHM). Phase noise measurements indicate that timing jitter was 2.5 ps at a pulse repetition rate of 223 MHz. Pulse-to-pulse amplitude fluctuations however, were significant and suggest that active cavity length stabilization may be required for reliable photoinjector applications.1998 Elsevier Science B.V. All rights reserved.At many electron accelerators throughout the world, there is great interest in developing high duty factor, high average power ('1 W) laser systems with picosecond pulsewidths and repetition rates synchronized to the accelerating cavity RF frequency [1]. Such a laser system can be used to extract electrons from a high-voltage semiconductor-photocathode electron gun during the portion of the RF cycle when electrons are accelerated into the machine. In this way, all of the photoemitted electrons are accelerated and delivered to the ultimate user of the beam; none are wasted as is the case when a DC laser light source is used to create

Development of a high average current polarized electron source with long cathode operational lifetime

“…Mode-locked Ti:sapphire lasers offer considerably higher power than the MOPA diode lasers, but commercial systems delivering picosecond pulses and pulse repetition rates above 120 MHz were not available at the time of our work. We developed a harmonically mode-locked Ti:sapphire laser to overcome the power limitations of the MOPA lasers [41]. Mode locking was obtained by introducing light from a gain-switched diode laser into the Ti:sapphire laser cavity, as shown in Fig.…”

Synchronous photoinjection using a frequency-doubled gain-switched fiber-coupled seed laser and ErYb-doped fiber amplifier

“…The optical pulse train was easily phase locked to the accelerator but output power was limited to 50 mW, not enough to provide the required 100 A of highly polarized beam from high polarization photocathode material. To address the power limitation of the diode MOPA system, a novel harmonic-modelocked Ti-sapphire laser was invented [9]. This laser satisfied the optical power requirements and could be wavelength tuned to provide maximum beam polarization, but the output beam was noisy which introduced undesirable highfrequency amplitude modulation on the extracted electron beam.…”

Very high voltage photoemission electron guns

“…The RF was derived from the accelerator master oscillator. This scheme has produced >2 W average power pulse trains stably locked to the accelerator RF at rates between ~200 MHz and 3 GHz [13].…”